Various types of gas sensors are installed in the exhaust pipe (pipe) of a vehicle in order to detect a specific gas component (NOx, for example) contained in exhaust gas. These types of gas sensors are generally installed in a specific pipe, such as the pipe 6 of the present invention shown in FIG. 1.
In the context of the present invention, a gas sensor 10 includes a sensor element 1 having a function of detecting NOx or the like, and a housing 5 which contains the sensor element 1 therein and includes a thread section 2 outside the housing and a sealing surface 4 which can form a sealing section 3 by coming in contact with a specific area of an installation section (boss 7). The boss 7 having a thread groove which can be screwed together with the thread section 2 of the housing 5 is secured to the pipe 6 in which the gas sensor 10 is installed. The gas sensor 10 is installed in the pipe 6 by screwing the housing 5 into the boss 7. As shown in FIG. 2, the sealing section 3 may be formed in a state in which a gasket 8 is disposed on the sealing surface 4 when installing the gas sensor 10.
As shown in FIG. 3, there may be a case where a rotating member (rotational hexagon 15), which can be rotated concentrically with the central axis of the housing 5, is disposed outside the housing 5, and the gas sensor 10 is installed so that the sealing surface 4 is pressed against the boss 7 by screwing the rotating member without rotating the housing 5. In the case of using the rotational hexagon 15, the sealing section 3 may also be formed in a state in which the gasket 8 is disposed on the sealing surface 4 in the same manner as shown in FIG. 2 (see FIG. 4).
Conventionally, in the case where the gas sensor is installed in the installation section by screwing the housing at an appropriate tightening torque, the installation area of the gas sensor may be subjected to high temperature when the temperature of the pipe is increased. For example, in the case where the gas sensor is installed in the exhaust pipe of a vehicle, the installation area of the gas sensor is subjected to a high temperature of 800-900° C. In this case, depending on the combination of the material for the boss and the material for the housing or gasket, a gap is easily formed at the sealing section under high temperature conditions due to the difference in coefficient of thermal expansion between the materials.
If a gap is formed at the sealing section, the tightening force of the screw is gradually decreased as the gap is increased. If the gas sensor is continuously used in a state in which the tightening force of the screw is decreased, the gas sensor may be dislodged from the pipe. In particular, since the possibility of dislodgement of the gas sensor is increased when used in an installation environment in which vibration is applied either continuously or intermittently, measures for eliminating such problems have been demanded.
The present invention has been achieved in view of the above-described problems in the conventional art. Accordingly, an object of the present invention is to provide a gas sensor which rarely allows the tightening force of the screw to be decreased even if the gas sensor is used under high temperature conditions when installed in a vehicle or the like, and is rarely dislodged from the pipe or the like in which the gas sensor is installed even if vibration is applied, a gas sensor installation structure equipped with the gas sensor, and a method for installing gas sensor.